Evidence of Evolution Comparative Anatomy
Comparative Anatomy • Comparative anatomy includes vestigial structures, skeletal structures, DNA, and embryology. • Comparisons of anatomical features in different organisms often provide evidence of change over time, as organisms are often classified together according to similarities in their structures. • It was through comparing the anatomy of organisms that scientist discovered phylogeny, meaning the evolutionary history of a group of organisms.
Vestigial Structures • Vestigial structures provide evidence of change. • Vestigial structures have no function in one species but may continue to function in another. • These organs are usually dwarfed. • Sometimes vestigial organs may be adapted for new uses • Even though organisms have these organs there is no significant disadvantage to the organism. • Examples of these include: • The human appendix which is useless in humans, but in other mammals it is necessary for digestion of high cellulose diet. • The human external ear muscles. • The tail bone. • Wisdom teeth. • Some snakes have skeletal limbs. • Hind limb structures embedded deep in their bodies • Penguin wings that cannot be used for flying but are adapted for swimming
Skeletal Structures • Skeletal structures, also known as homologous structures, are structures that share a common origin but may serve different functions in modern species. • These structures are evidence that organisms with similar structure evolved from a common ancestor. • Examples include the forelimbs of a variety of mammals. For example, human, cat, whale and bat. • These species show the same skeletal elements, as in the humerus, radius and ulna. • However these skeletal elements have been modified over time to suit the different functions suitable for the type of mammal.
DNA • Scientists hypothesize that if all organisms living today evolved from a common ancestor, they should have similar genetic material. • Species appearing to be close relatives should have greater similarities in their chromosomes and DNA than species appearing to be distant relatives.
Embryology • Embryology of organisms can be used to demonstrate the existence and even degree of relatedness of organisms. • In the early stages of development embryos of many organisms look extremely similar. • Embryos in mammals, birds, reptiles and fish have many body similarities in common e.g. Gill slits, two chambered heart, and tail. • As the embryos develop further, the similarities gradually disappear. • This embryonic resemblances indicate that organisms are related by their common ancestors.